Experimental Measurement Results on TOBUMOS First Run
TOBUMOS devices are fabricated together with TOB-Diode on the same wafer. Unfortunately, the first separate run of TOBUMOS fabrication was not fully successful. Though the fabricated TOBUMOS shows good IV characteristics and improved specific on-resistance under certain Control voltage, it was found that the breakdown voltage is always about 30 V and the breakdown measurement is unrepeatable. By performing the electrical test and analysis on Gate region, the Gate oxide breakdown near termination region was suspected. Therefore, follow-up efforts were performed in order to solve the problem of premature breakdown.
Fabricated TOBUMOS was tested having normal IV characteristics. Figure 10.33 shows the Drain current vs Drain voltage on wafer # 06 at different Gate voltages from 0 V to 10 V at 1 V interval, without Control
Fig. 10.33. IV characteristics of TOBUMOS with W = 4.0 дш, Wob = 1.5 дш, and Lg = 0.8 дш (refer to Table 10.4) on wafer #06 at Vgs in the range of 0-10 V.
voltage. Measured threshold voltage as in Fig. 10.34 is about 2 V, which is higher than the simulated value of 1.2 V.
Tuning Effects on TOBUMOS
It was found that by applying positive voltage on Control electrode, the on-state performance of TOBUMOS is enhanced. As given in Fig. 10.35, the plots of IV characteristics of TOBUMOS under 20 V Control bias are shown in comparison to the original IV performance without external bias. The enhanced Drain current under bias can be obtained in both the linear region and the saturation region of the MOSFET. The enlarged IV curve at Vgs = 10 V at smaller Vds below 0.1 V is shown in Fig. 10.36. Obviously, with the augment of Ids, on-state resistance is improved when increasing the Control bias from 0 to 20 V and the decrease is larger between 0 and 10 V compared to that between 10 and 20 V Control bias.